We've been getting by leaving the gray tank valve open. I bought a knockoff flush king and have been using that to wash the hose after dumping the black tank. Replacing the air introduction valve in the kitchen didn't solve the problem.
We did fill the gray tank to capacity, as I forgot once to open the gray tank valve after dumping the black. Water backed up into the pipes, which called attention to a leak at the P trap under the kitchen sink. The flange that mates to the second end of the P trap was cracked. After cutting the old pipe out (thanks FR assembly workers for forgetting to use a screw-in piece
) and getting an adapter to use standard off the shelf stuff, it was fixed. Haven't had a smell yet, but I'm not holding my breath. I'll keep you all posted if this cures the smell.